The present invention is related to an electronic stroke monitor for a vehicle brake. More specifically, the present invention is related to an electronic stroke monitor of an air disc brake for use on a heavy duty truck.
The number of miles traveled by heavy-duty trucks and passenger busses increases significantly every year. Because the size of passenger cars being driven has become smaller due to the increased price of gasoline, it has become increasingly necessary to ensure the proper performance of brake actuators and brake systems of these heavy-duty vehicles to provide the truck operator every opportunity to avoid a loss of control. Therefore, various systems have been developed to monitor the stroke of a brake actuator for use on drum brakes widely used in industrial trucking.
However, on heavy-duty passenger vehicles, such as, for example, busses, the use of air disc brakes is becoming more popular. To date, a viable brake monitoring system for use on an air disk brake has not been developed.
Brake monitoring systems used on air drum brakes are directed toward monitoring the length of stroke of a pushrod projecting from inside a chamber of the brake actuator. The monitoring enables the user to determine if the brake actuator is functioning properly, is subject to an over-stroke condition, or is subject to a hanging or dragging brake condition. Monitoring these conditions by monitoring the stroke of the pushrod is possible because the pushrod of the brake actuator is fixedly attached to the actuation device of the drum brake. In the case of a hanging or dragging brake, the actuation device of the drum brake is immobilized in an actuated position preventing the pushrod from returning to an un-actuated position when the brake pedal is released by the vehicle operator.
However, the pushrod of an air disk brake actuator is not fixedly attached to the lever arm of a caliper that actuates the disk brake. Therefore, should a hanging or dragging brake condition occur, the lever arm becomes separated from the pushrod rendering the type of monitoring system used on a drum brake non-functional for a disk brake. An electronic sensor that monitors the stroke of the pushrod senses that the pushrod has returned to its un-actuated position and incorrectly senses that the brake is operating normally. Furthermore, it is impossible to verify function of the actuator or the caliper without separating the two devises to perform a manual inspection. Still further, it is impossible to determine if the two devices remain pneumatically sealed where necessary to prevent entry of environmental contamination from causing the caliper from functioning properly. Therefore, it has become necessary to develop a vehicle brake monitoring assembly that is capable of identifying and distinguishing between an over-stroke condition and a hanging brake condition of an air disk brake.
Additionally, the caliper housing is sealed to a boot disposed inside the brake actuator to prevent environmental contamination from entering the caliper, which is known to cause mechanical defects to the components disposed inside the caliper resulting in brake failure. Presently, a determination of the integrity of the air-tight-seal between the caliper housing and the brake actuator is impossible. Therefore, it would be desirable to provide the ability to determine if the integrity of the air-tight-seal has been maintained or remains uncompromised.